Known lane departure prevention control detects travel section lines that are marked on a road, and controls a steering device such as to prevent a vehicle from departing from its traffic lane. With this control, in order to control the vehicle to follow curvature of the road, a steering angle sensor detects the steering angle of the steering device of the vehicle, and feedback control is executed to bring the steering angle to a target value.
In executing such feedback control, a deviation of the neutral point of the steering angle sensor, i.e. a deviation of a detected value of the steering angle may make the actual steering angle become excessively large or become excessively small in relation to the curvature of the road.
A neutral point learning device described in PTL 1 has been proposed as a solution for this issue. With the neutral point learning device of PTL 1, when detection values from the yaw rate sensor indicate that the vehicle is traveling along a straight line, the detected value of the steering angle is taken as the neutral point of the steering angle sensor.